1. Field of the Invention
The present invention relates to an image reading apparatus used for reading out images printed on a document sheet for example. The present invention also relates to an illuminator used for such an image reading apparatus.
2. Description of the Related Art
As is well known, devices such as an image scanner and a facsimile machine incorporate an image reading apparatus for reading out images printed on a document sheet. FIG. 23 of the accompanying drawings shows, in section, a conventional contact-type image reading apparatus. The illustrated apparatus includes a resin casing 10e formed with an inner space lie. The casing 10e has a rectangular configuration elongated in the primary scanning direction.
A rectangular substrate 2e, which is also elongated in the primary scanning direction, is fixed to the bottom of the casing 10e. As shown in FIG. 24, the substrate 2e carries a plurality of light sensors 20e arranged in a row extending in the primary scanning direction. The substrate 2e also carries a plurality of light sources 21e (such as light-emitting diodes for example) which are spaced from each other at regular intervals in the primary scanning direction.
Referring back to FIG. 23, the conventional image reading apparatus 1e is formed with an opening 12e held in communication with the inner space 11e. A transparent cover 3e is fitted into the opening 12e. 
A platen P is provided above and held adjacent to the cover 3e for forwarding a document D to be read out. An image reading line L extends on the cover 3e in facing relation to the platen P. Between the image reading line L and the light sensors 20e is provided a lens array 4e. 
In the conventional image reading apparatus 1e, when the platen P is rotated, the document D, which is held in sliding contact with the cover 3e at the image reading line L, is forwarded. During this operation, the document D is illuminated, at the image reading line L, by light emitted from the light sources 21e. Then, the light reflected on the document D passes through the lens array 4e to be received by the light sensors 20e. Finally, each of the light sensors 20e will output analog image signals based on the received light.
The image reading apparatus described above has been found disadvantageous in the following point.
As shown in FIG. 24, the light sources 21e are spaced from each other at predetermined distances. In this arrangement, the luminosity at each point on the image reading line L cannot be uniform. Specifically, as shown in FIG. 25, the luminosity becomes greatest at particular points on the reading line L that are closest to the respective light sources 21e, whereas it becomes weaker between these particular points.
When the luminosity along the reading line L is nonuniform, as stated above, it is difficult or even impossible to obtain proper image signals from the light sensors 20e. Clearly, the subsequent printing operation based on such improper image signals will not be performed properly. Under these circumstances, images to be reproduced on a recording paper sheet will unfavorably be different in appearance from the original images on the document.
The above problem may be overcome by increasing the number of the light sources 21e mounted on the substrate 2e. This solution, however, will give rise to another problem, i.e., higher production costs.
It is, therefore, an object of the present invention is to provide an image reading apparatus which eliminates or reduces the above-described problems.
Another object of the present invention is to provide an illuminator advantageously used in such an image reading apparatus.
According to a first aspect of the present invention, there is provided an image reading apparatus for reading out images printed on a document comprising:
a casing formed with an inner space, the casing being elongated in a primary scanning direction;
a transparent cover supported by the casing, the cover being held in sliding contact with the document at an image reading line;
an insulating substrate attached to the casing;
a plurality of light sources mounted on the substrate for illuminating the image reading line, the light sources being arranged in a first row extending in the primary scanning direction;
a plurality of light sensors mounted on the substrate for receiving reflected light coming from the image reading line, the light sensors being arranged in a second row extending in the primary scanning direction; and
luminosity-adjusting means supported by the casing for equalizing luminosity along the image reading line.
According to a preferred embodiment of the present invention, the luminosity-adjusting means may include at least one luminosity adjuster for shielding part of light emitted from the light sources.
Preferably, the luminosity-adjusting means may include an additional luminosity adjuster for shielding part of light emitted from the light sources. The additional luminosity adjuster may be arranged below said one luminosity adjuster.
According to the preferred embodiment, the first-mentioned one luminosity adjuster may be provided with a plurality of protrusions arranged in the primary scanning direction. Each of the protrusions is arranged to positionally coincide with one of the light sources in the primary scanning direction.
Preferably, each of the protrusions may have a triangular configuration. Alternatively, each of the protrusions may have a smooth, wave-like contour, or have a rectangular configuration.
According to a preferred embodiment, the luminosity-adjusting means may be formed integrally with the casing.
According to another preferred embodiment, the luminosity-adjusting means may be formed separately from the casing.
According to a preferred embodiment, the luminosity-adjusting means may include at least one luminosity adjuster for allowing part of light emitted from the light sources to exit from the inner space of the casing.
In the above instance, said one luminosity adjuster may be provided with a plurality of protrusions arranged in the primary scanning direction, each of the protrusions being disposed between two adjacent light sources in the primary scanning direction.
According to a preferred embodiment, the luminosity-adjusting means may include a plurality of first reflective partitions spaced from each other in the primary scanning direction. Each of the first reflective partitions is disposed between two adjacent light sources.
Preferably, each of the first reflective partitions may have a reflectance of 90-98%.
Preferably, the luminosity-adjusting means may further include a plurality of second reflective partitions, each of the second reflective partitions being disposed above a corresponding one of the light sources.
Said each of the second reflective partitions may have a bottom surface spaced from said corresponding one of the light sources by a predetermined distance.
Preferably, the bottom surface of said each of the second reflective partitions may have a reflectance of 90-98%.
According to a second aspect of the present invention, there is provided an illuminator comprising:
a plurality of light sources arranged in a line extending in a predetermined direction; and
a plurality of first reflective partitions spaced from each other in the predetermined direction, each of the first reflective partitions being disposed between two adjacent light sources.
Preferably, said each of the first reflective partitions may have a reflectance of 90-98%.
Preferably, the illuminator may further comprise a plurality of second reflective partitions each of which is disposed above a corresponding one of the light sources.
Other objects, features and advantages of the present invention will become clearer from the detailed description of preferred embodiments given below with reference to the accompanying drawings.